(1) Field of the Invention
This invention generally relates to tape threading devices, especially those used in magnetic tape drive systems. More particularly this invention is concerned with devices for restoring and removing tape leader blocks to and from the leader block housings provided for such leader blocks in most tape cassettes.
(2) Description of the Prior Art
Various devices have been developed for automatically threading tapes from supply reels, past transducer heads, and on to take-up reels. One widely used tape threading device is disclosed in U.S. Pat. No. 4,399,936 ("the -936 patent"). In the case of magnetic tapes, the tape is usually dispensed from a tape cassette by a pulling action upon a leader block. This pulls the leader block out of the cassette's leader block housing. This in turn pulls the tape out of the cassette. The leader block is restored back into the cassette's leader block housing by pushing upon the leader block, preferably while the tape is being rewound. Most leader blocks are housed in a diagonal orientation with respect to one corner of an otherwise rectangular-shaped tape cassette. U.S. Pat. No. 4,383,660 ("the -660 patent") well represents this kind of tape cassette system. The leader block is held in the leader block housing by means of a cantilevered arm which forms a part of the front surface of the tape cassette. The cantilevered arm usually has a rounded edge which engages a rounded lip boss on the underside of the front of the leader block. This engagement is in the nature of a compression fit between the rounded edge of the cantilevered arm and the rounded lip boss of the leader block. In effect, the cantilevered arm acts as a projecting leaf spring which positions the leader block within the cassette housing. As is well illustrated in FIGS. 3a, 3b and 3c of the -660 patent, a pulling force upon the leader block will disengage it from the leader block housing. In effect, the rounded edge of the cantilevered arm will be lifted slightly upward by a lifting force transmitted to the leader block's lip boss. This lifting force is provided by a rearward pull of the threader pin. Assuming sufficient pulling and lifting forces, the rounded lip boss of the leader block will slide past the rounded edge of the cantilevered arm and thereby permit the complete withdrawal of the leader block from the leader block housing. Conversely, a pushing force upon the leader block will cause the rounded lip boss of the leader block to slide inwardly past the rounded edge of the cantilevered arm and thereby restore the leader block to a snug fit within the cassette's leader block housing.
Restoration and removal of the leader block from the cassette's leader block housing also presupposes an initial successful coupling of the threader pin with the threader pin receiver in the leader block. Therefore, an understanding of certain problems encountered in the coupling and uncoupling of threader pins and leader blocks also will provide a further appreciation of the device disclosed in this patent application. We can begin by first noting that the threader pin of our device could have various configurations. For example, it could be presented in the form of a ball suspended from a rod, a cylinder suspended from a rod, etc. In any event, the forward ends of the leader blocks are usually provided with receivers which are presented in the form of openings or slots which are highly compatible with the configurations of the threader pins employed. Most threader pins currently in use have a relatively short enlarged cylindrical member whose diameter is greater than that of a more elongated rod-like top portion of the threader pin which in turn is attached to the underside of the threader arm.
Threader arm devices such as the one disclosed in the -936 patent usually deliver their associated threader pin directly to the leader block under the power and action of the gear motor torque which is delivered to the threader arm. That is to say, the threader arm's gear motor torque is employed both to thread the tape through the tape deck system and to restore and remove the leader block to and from the cassette's leader block housing. The restoration and removal operations cause a great deal of wear upon the gear motor system in their own right. Moreover, the other threading operations that these prior threader arm devices are called upon to perform represent another source of gear motor wear. Eventually, wear from all such sources leads to threader arm motor/gear train failures and/or failures due to certain threader pin/leader block misalignments. They are made more pronounced by the fact that delivery of the threader pin to the leader block represents the final phase of a powered rotation of the threader arm in these prior art devices. This final phase of the threader arm's rotation must, however, be carried out very accurately. Any substantial misalignment between the incoming threader pin and the leader block's receiver slot will cause the threader pin to miss the receiver slot and collide with inappropriate parts of the leader block. Such wear is perhaps the largest single factor in producing collisions due to threader pin/leader block receiver misalignments. Such malfunctions are usually exacerbated by the fact that the threader pin approaches the leader block's receiver slot at rather high rates of speed. Thus, misalignment often produces a violent collision of the threader pin on the edge of the leader block's receiver slot rather than a smooth, assured coupling of these two parts. However, slower threader arm speeds are not a particularly viable solution to the problem. Threader arms need enough torque to restore and remove the leader block to and from their cassette housing; and they need certain speed and monentum attributes in order to pull the tape through the remainder of the rather circumvoluted paths they often must follow between the supply reel and the take-up reel. Consequently, most prior art threader arms are usually designed and powered much more by considerations associated with pulling the tape through a convoluted tape deck path than they are by considerations associated with some eventual collision of the threader pin upon some inappropriate part of the leader block.